Wheat is a major cereal grain crop of Pakistan, which
meet food needs of growing human population of the country. Wheat is
grown in rabi season. This crop needs cool season for emergence or
growth and warm season for the maturity. Whereas, most of the broad
leaved weeds also make growth during the cool season and compete with
wheat crop for nutrition and other inputs.

The use of pure seed, proper land preparation,
balanced fertilizer and proper irrigations along with weed control play
vital role for higher wheat yield. Weeds emerge as un-invited plants,
which are harmful not only for whole eco-system but for the environment
where are grown. Some weeds are poisonous and some are useless plants
exists on the land and compete crop plants by taking food nutrients,
water, sunlight and other elements and weakens the main crop, which
results in low crop yield.

For achieving higher wheat production, new wheat
varieties, modern methods of sowing and control of harmful insect pests
and diseases are important but yield target may hardly be accessible.
The main reason behind it is that the growers are paying little
attention to the weed control or using eradication practices of weeds,
due to that yield loss may occur. This sort of loss of wheat grains due
to weeds may be 15 to 25 per cent.

Timely control of weeds is most essential for better
wheat production, weeds are crop pests of destructive nature, which need
continuous strategy to eradicate them. Weed competition with crop for
food, water, sunlight, air etc. extends from 3 to 8 weeks. Thus, weeds
must be controlled during the period of their competition for better
crop and increase in its production. If not doing so, and weeds were
left to grow during full season in the crop land, the yield would
decrease at drastic level.

Weeds of wheat:
There are about thirty weeds of
wheat found in Sindh, which are spreaded over in a few or large numbers
under different wheat growing areas. Whereas, twelve to sixteen weed
species come up and grow in wheat fields, which induce losses upto
economic threshold level (Table 1). Such weeds lower the production
capacity of land, by competing in irrigation, plant nutrients, sunlight,
air and growing space, and left wheat crop devoid of those inputs. The
result is that wheat plants turn weak and produce low grain yields.

Table
1:Weeds of wheat

Sr. No.

Local Name

English Name

Botanical Name

Family Name

1.

Jhil

Lamb's quarter

Chenopodium album

Chenopodiaceae

2.

Sinjh

White sweet clover

Melilotus alba

Leguminosae

3.

Kurund

Nettle leaf weed

Chenopodium murale

Chenopodiaceae

4.

Basri

Wild onion

Asphodelus tenuifolius

Liliaceae

5.

Bili booti

Shepherd's clock

Anagallis arvensis

Primulaceae

6.

Dhanak

Canary grass

Phalaris minor

Graminae

7.

Jhangli Jai

Wild oat

Anena fatua

Graminae

8.

Matri

Vetch weed

Vicia hirta

Leguminosae

9.

Maino

Wild medic

Medicago dentatus

Leguminosae

10.

Jhangli Palak

Sheep sorrel

Rumex dentatus

Leguminosae

11.

Kanderi

Wild safflower

Carthamus oxyacantha

Compositae

12.

Chabbar

Lawn grass

Cynodon dactylon

Graminae

13.

Kabah

Sedge nut grass

Cyperus rotundus

cyperaceae

14.

Naro

Bind weed

Convolvulus arvensis

Convolulaceae

15.

Kandero

Camel thorn

Alhaji Camelorum

Papilionaceae

16.

Drubh

Deep root grass

Desmostachya bipinnata

Graminae

Growth losses of weeds in wheat

* Weeds reduce growth by making share in water,
food, light and sir.* Weeds reduce tiller production and survival, which may result
in low production.* Weeds grow fast and shade over the wheat plants, which may
result in weak crop stand.* Weeds reduce growth, production and grain quality of wheat by
mixing at the time of harvest.* Weeds make hinderances and reduce water flow applied to the
wheat.* Some weeds induce lodging of wheat crop by binding climbing
over the plants.* Some weeds due to spines and thorns make trouble or
difficulties in the crop harvest.

Production losses of weeds in wheat:
Weed losses in wheat
may occur from initial stages to the last stage of maturity, harvest, Threshing,
winnowing and storing of wheat grains. Weeds of wheat such as, wild oat and
phalaris minor have close resemblance to the wheat crop, which could not be
identified during early growth stages, affect crop growth and reduce wheat
yields. Weed plants are more resistant, hardy and making faster growth than
wheat. Because, until when, wheat plants establish before that weeds bind over
the plants and wheat crop receive less time for growth, which result in
reduction in production of the crop. Some weed species, nourishes insect pest
and diseases and provide shelter to them.

In wheat weeds, there are species of weeds, which bear thorns
(such as camel thorn, prickly poppy etc.) and create difficulties in harvest and
produce losses in grain quantitatively. Whereas, Bind weed is such a species
that binds over the wheat and therefore, the losses of crop growth and yield
occur. Some weeds of wheat (such as wild onion and white sweet clover) produce
odourful seeds, which spoil the quality of flour.

Weed control methods:
There are different methods of
controlling weeds of wheat, including traditional to improved weed control
methods. The collectively weed control methods depends upon cropping pattern,
economic status of the farmer, technology adopted, crop growing area and its
climatic conditions.

The weed control methods by and large consists of cultural,
mechanical, biological, chemical and integrated weed management practices. The
forming communities of Pakistan both due to small holdings prefer to use
cultural and chemical methods, which are the most common, effective and
important weed control methods in our conditions for the control of weeds of
wheat.

Cultural weed control:
The cultural weed control method
is more effectively used in wheat growing areas, due to the reason that it is
observed as environment friendly method of weed control and it is farmer's
method who uses their various agricultural practices to eradicate weeds. This
method may be used with stirring soil through weeding and interculturing
practices by using Hoe (khurpi), Pick axe (chanjour) and spade etc. In normal
course, the farmers in a majority control, prevent or eradicate weeds through
cultural practices including deep tillage, flooding, crop rotation, hand
pulling, hoeing, weeding and interculturing with tools and implements. The
cultural weed control method has its scope, by means of that weeds could be
uprooted, the soil be opened and pulverized through breaking up of hard pan,
weeds after removal may be incorporated in the soil for adding organic matter,
which would enhance fertility and water holding capacity of the soil.

In wheat, the control of weeds may necessarily be done before
first irrigation application by cultural method i.e. Interculturing practice. It
would not only clean wheat field from the weeds but such stirrer soils would
retain moisture for longer periods for proper crop growth.

Bar harrowing is one of the important practice under cultural
weed control, which may be done by Bar harrow that run after first or second
irrigation when soil comes into condition using bullocks to drag this implement.
Bar harrow would perform the function of interculturing alongwith uprooting
weeds.

Wheat grown on large areas needs harrowing operation to
control weeds, which is an economical cultural practice by the use of Bar
harrows. Such practice may be employed to break hard pan of soil and to control
weeds in wheat. Bar harrow opens root zone of wheat during early growth stages
of the crop, which would result in better root establishment of wheat. Harrowing
would bring better environment for wheat through retaining moisture for longer
time. This would maintain vigorous growth and increase in crop yields. It is to
be noted that Bar harrow could only be used when crop is grown by drilling
method. By this means, wheat crop may be kept clean from annual weeds such as
lamb's quarter, white sweet clover, nettle leaf weed, wild onion, shepherds
clock, vetch weed etc.

However, the pre-sowing practices such as clean seed, proper
land preparation, increasing seed rate, timely sowing, crop rotation and
competition may bitterly adopted to control weeds of wheat.

Chemical weed control:
The chemical weed control is one
of the improved method and recent technology to have control over weeds. In
wheat, the most easy and cheap method is use of weedicides, which take less time
and is effective input to control weeds on large scale. There are number of
weedicies, which have been effective and profitable while controlling weeds of
wheat. Because, chemical weed control is more efficient to control weeds in
wheat when it is grown on large area.

The use of
herbicides/weedicides for the control of weeds is
rapidly increasing. In technical terms, the control of weeds through herbicides
is known by chemical weed control technology. For this purpose, specific or many
kinds of weedicidies are formulated and are under use, which have been very
effective to control annual and perennial weeds (Table 2).

The weedicides are considered effective and efficient in
terms of their selection, volume, application on specific weed and/ or crop. It
also be remembered that weedicides are poisonous and must be handled carefully,
which may be dangerous to plant or animal life, human health and life, all
living beings and environment as a whole.

The weedicide application would be essential when the losses
of weeds increase at economic threshold level. In wheat, weed density and
species, which cause production losses must be monitored before application of
weedicides. The time and method of herbicide application may be classified in
three categories:

Pre-planting application:

The herbicides applied before sowing of wheat crop.

Thus, pre-planting herbicides are used on the prepared land
before growing crop, which would kill newly emerging weeds.

Pre-emergence application:

One herbicides applied before emergence of either crop or
weed species which may be effective to control weeds, In this case, spray is to
be done after sowing of crop and before emergence of weeds.

Post-emergence application:

The herbicides applied after emergence of both either crop or
weed species. In this case, weeds would have been emerged and are sprayed on
their leaves.

Weeds must come under farmer's target to be controlled during
early stages of crop growth for the decrease of yield losses. Thus, weed control
technology of wheat must reflect in terms of its benefits and losses on crop
productivity. If weeds are controlled upto first 4, 6, 8 and 12 weeks after
sowing, there would be yield increase of 21.5, 39.5. 46.5 and 55.0% and if weeds
are kept clean from wheat crop for full season, there would be yield increase of
65.5% .